The present invention relates to a data communications method and apparatus and in particular to a method and apparatus which make use of a switching centre having a plurality of data network access servers.
The conventional way for a home user of a personal computer (PC) to access the Internet is to set up a telephone call, via his telephone operator, to an Internet service provider. The service provider allocates an Internet address to the PC (xe2x80x9csubscriber terminalxe2x80x9d) for the duration of a session and acts as a protocol converter for data transmitted between the Internet and the subscriber terminal.
More recently, it has been proposed to combine the functionality of the Internet service provider into certain exchanges of the telephone network. An advantage of this is that the subscriber need only receive a single bill for both telephone calls and Internet access.
Exchanges provided with this facility are accessed by subscribers dialing a predefined access number. The exchanges contain xe2x80x9cintelligencexe2x80x9d which enables them to recognise that a call received to this number is an Internet access requests. In response, the exchange provides a connection between the subscriber terminal and the Internet via one of a number of so-called Internet Access Servers (IASs)xe2x80x94alternatively known as Network Access Servers (NASs).
The connection between the subscriber terminal and the IAS is a circuit switched connection, i.e. occupying reserved bandwidth, and utilises a Point-to-Point Protocol (PPP) such as is defined in RFC 1661. The reserved bandwidth comprises one Integrated Services Digital Network (ISDN) traffic channel (B-channel) providing a bandwidth of 64 Kbits/sec.
The number of IASs provided at an exchange determines the Internet access capacity of the exchange. However, using PPP, the bandwidth which can be accessed by an individual subscriber is limited to 64 Kbits/sec (i.e. one ISDN B-channel).
A Multilink PPP (RFC 1990 (1717)(1934)) has been proposed in order to provide further transmission bandwidth to subscriber terminals. This protocol uses a combination of two or more connections to provide a single larger channel. Considering for example the situation where the subscriber line to the exchange makes use of the Integrated Services Digital Network (ISDN) user-network interface, it is possible to make use of both of the communication B-channels available on the subscriber line for Internet access.
This works satisfactorily as long as all of the individual B-channels making up the multilink channel terminate at the same IAS. However, Multilink PPP cannot operate where individual B-channels are provided via different IAS, as the order of data packets sent between the Internet and the subscriber terminal may be lost due to variations in the transmission delays between different B-channels. Also, IP does not provide a mechanism whereby packets having the same IP address can be sent to different IASs.
It often transpires that when a low bandwidth access has been provided to a subscriber terminal, and that terminal subsequently requests additional bandwidth (i.e. using Multilink PPP), the allocated IAS cannot provide that bandwidth and multilink access cannot therefore be provided. Whilst it is possible to always reserve spare capacity on an IAS for a subscriber terminal already allocated a channel on that IAS, this may be wasteful of bandwidth resources.
This problem could be alleviated by increasing the capacity provided by an IAS. However, capacity is a function of processor power, power consumption, board size, etc. and cannot easily be achieved. An alternative solution which has been proposed involves connecting several IASs (which are usually provided in the form of printed circuit boards loaded into racks of an exchange) to a common multilane cell bus. The disadvantage of this solution is that the number of IAS which can be connected together in this way is limited (due to limits imposed by the capacity of the common bus) and also that a new inter-IAS communication protocol is required.
It is noted that similar problems arise in connecting a subscriber terminal to other types of data networks via data network access servers, where it is desired to utilise a multilink PPP.
It is an object of the present invention to overcome or at least mitigate the above noted disadvantages. In particular, it is an object of the present invention to provide a switching centre for connecting a user terminal to a data network using a multilink point-to-point data communications protocol.
According to a first aspect of the present invention there is provided a method of connecting a terminal to a data network, wherein the connection is made through one of a plurality of data network access servers coupled to the data network, the method comprising:
receiving an initial data network access request from the terminal, the request being directed to a first address predefined at the terminal;
in response to said initial request, allocating to the terminal a first transmission channel on one of the data network access servers for which the in-use fraction of the communication bandwidth is less than a predefined fraction;
delivering to the terminal a new data network access address;
receiving a subsequent access request from the terminal directed to said new address;
in response to said subsequent request, allocating to the terminal a further transmission channel on the data network access channel on which said first channel is already provided, even if the in-use fraction of the communication bandwidth of the data network access server exceeds said predefined fraction.
By ensuring that transmission bandwidth for a given terminal is always allocated on a single data network access server, embodiments of the present invention ensure that multilink point-to-point protocol can be used as the communication protocol between the terminal and the data network. Furthermore, by preventing access to a certain reserved fraction of the capacity of each network access server for first time requests, embodiments of the invention increase the probability that capacity will be available at a given network access server for multilink point-to-point protocol.
In certain embodiments of the invention, the data network is a wide area network such as the Internet, in which case the data network access servers are Internet access servers.
The network access servers may be provided at a single switching centre to which access requests from the subscriber terminal are directed. Alternatively, the network access servers may be distributed over several switching centres, where access requests are forwarded between switching centres depending upon demand.
The or each switching centre at which the data network access servers are provided may be an exchange of a telephone network in which case the terminal may be connected to the exchange(s) via a telephone line of the telephone network or via a wireless telephone communication channel. Preferably, said first and said new addresses are telephone numbers (B-numbers) which can be called by the terminal (see for example ITU-T, I.331,E.164).
The terminal may be connected to a further data network, e.g. a Local Area Network (LAN), and through that network to the switching centre(s).
The terminal may be a subscriber terminal on which is run a user application, e.g. a Web browser. Alternatively, the terminal may provide a routing functionality for other, end-user terminals connected to the first mentioned terminal by a Local Area Network (LAN) or a Wide Area Network (WAN).
According to a second aspect of the present invention there is provided apparatus for connecting a terminal to a data network, the apparatus comprising:
a plurality of data network access servers coupled to the data network;
first receiving means for receiving an initial data network access request from the terminal, the request being directed to a first address predefined at the terminal;
first control means arranged, in response to said initial request, to allocate to the terminal a first transmission channel on one of the data network access servers for which the in-use fraction of the communication bandwidth is less than a predefined fraction;
transmission means for transmitting to the terminal a new data network access address;
second receiving means for receiving a subsequent access request from the terminal directed to said new address; and
second control means arranged, in response to said subsequent request, to allocate to the terminal a further transmission channel on the data network access server on which said first channel is already provided, even if the in-use fraction of the communication bandwidth of the data network access server exceeds said predefined fraction.
In one embodiment of the above second aspect of the present invention, the data network is the Internet and said data network access servers are Internet access servers. Preferably, the apparatus comprises a plurality of switching centres amongst which the Internet access servers are distributed. More preferably, the switching centres are exchanges of a telephone network, and the network comprises a telephone line, or wireless radio telephone link, coupling the terminal to the exchanges.